ABSTRACT
OBJECTIVES: The objective of this study was to determine the quantitative influence of vitamin K epoxide reductase complex subunit 1 (VKORC1) and cytochrome P450 2C9 (CYP 2C9) polymorphisms on warfarin dose requirements in Turkish patients. METHODS: A total of 205 patients taking warfarin for >2 months were enrolled in the study. Deoxyribonucleic acid (DNA) samples from these patients were genotyped for polymorphisms in VKORC1 and CYP2C9 genes. A linear regression analysis was used to determine the independent effects of genetic and non-genetic factors on mean warfarin dose requirements. RESULTS: The VKORC1 promoter polymorphism (3673 G>A) was associated with differences in weekly mean varfarin dose: for GG genotype the dose was 43.18 mg/week, for GA genotype 33.78 mg/week and for AA genoype 25.83 mg/week (P < 0.0001). Patients who carried VKORC1 and CYP2C9 variants needed a 40% lower mean weekly warfarin dose compared to wild types. Variables associated with lower warfarin dose requirements were VKORC1 3673 AA or GA genotype (both P < 0.0001), one or two CYP2C9 variant alleles (both P < 0.0001), increasing age (P < 0.0001) and non-indication of venous thromboembolism for warfarin therapy (P = 0.002). CONCLUSION: Polymorphisms in VKORC1 and CYP2C9 genes were important determinants of warfarin dose requirements in Turkish patients.